Homebrew PCBs

I got it sorted out now. Was a bit confused by something I read on 
parallel ports. Its desciption made it sound like the port wasn't 
good at logic high and was really just limited to grounding or high 
resistance. I actually got out my multimeter and fired up the KCam 
demo just to see.

Looks like Enable is the only line I have to pull high and thats a 
safety issue.

--- In Homebrew_PCBs@yahoogroups.com, "Dave Mucha" <dave_mucha@y...> 
wrote:
> --- In Homebrew_PCBs@yahoogroups.com, "ghidera2000" 
> <ghidera2000@y...> wrote:
> > I'm just finishing up the design for an A3977SED based 
controller 
> > board but I'm a bit confused about the parallel port connections.
> > 
> > Can the parallel port drive logic high and low or does it just 
go 
> > active low (sinking) and high-Z? i.e. Do I need pullups to 
generate 
> > logic high, or can the parallel port handle this just fine?
> > 
> > I plan on pulling Enable high on the board and setting it to 
active 
> > low in the software. That way if the cable pops out I know the 
> > drives will stop.
> 
> I'm not following this exactly, but as I understand the step 
signals 
> are generated in software and pulse the chip.  the chip sees a 
high 
> or low as the pulse changes.  you do not have to alter that pulse 
> train.
> 
> dittor for direction.  you just swap one phase and it will run the 
> opposite direction.  again, no need to alter the pulse.  and also 
> canned CNC software has that function also.
> 
> Check the A3977 specs, I thing the chip needs around 1.5 volts on 
the 
> step or dir pins to change state.  since you do not need 5.0 
volts, 
> but mroe like 3.5 volts, you do not need the pull up or downs.
> 
> Dave